EI for low light setup


Junior Poster
Feb 23, 2009
Could you please direct me to some useful posts where EI is discussed for low light tanks? My setup will have CO2


Lifetime Charter Member
Lifetime Member
Jan 5, 2009
Washington, DC


Guru Class Expert
Feb 17, 2007
Lincoln, UK
If you have CO2 then just go by the amount suggested. Then drop the dose down 10% fortnightly until you see some negative response at which point move back up to the dose you did the week before.

I had low light (0.9WPG) and CO2 and I just dosed full EI with no problems.


Tom Barr

Staff member
Jan 23, 2005
I think many will point out that doing full EI and the full dosage with water changes is not harmful.

Some crazies and loonies like to say it is.

However, there is some pragmatic common sense advice added as well. EI is not meant to be used rigidly, no method is.
Some of these crazies suggest you must use another method due to the 50% water change and higher dosing.
No, you need not waste or do so many water changes.

You start high and then progressively reduce the dosing % as suggested by SuperColely1 for dosing ferts. This means there will be less and less build up each time to reduce the dosing and observe.
Once you see a negative effect on plants(or positive on algae), you bump the dosing back up to the next highest level, this is the tank's min demand for good non limiting growth. You can get away without any water changes if you are good at this.
Most are not and do not risk it, so they a water change every month or so. With non CO2, there's less risk and issue, so none are need other than to clean things up after a rare trimming perhaps.

It'd estimate maybe 1/3-1/2 EI for your tank would be fine. If you use a rich nutrient sediment, say ADA's Aqua soil or something.......then the lower end would be fine.
If you have a good current and higher fish stock level, then perhaps even less, 20-30% ranges.

Water changes are similar, I might only need to do a water change once a month on my 1.3-1.5W/gal tanks that use T5's and are placed 30cm above the tanks which are 60cm deep.
I still tend to do good sized water changes, they keep the tank clean, easier to work on them, trim etc, takes the same motivation to do 10% as it does 70%.
Frequency is less perhaps is the only difference for me.

You can also automate water changes or do a small amount each day or two etc.............some folks like engineering and techy automated stuff.
Same for dosing.

Then you mostly garden maybe once a month with lower light, feed fish, check CO2, clean filters etc.
Still, adding full EI does not harm anything, there's a wide user range. I still have not met anyone/or heard verified reports that has gone to the upper negative bounds for PO4, K+, or NO3, traces other than myself.
It's been 15 years or so........so I doubt it's a common occurrence or issue after this much time and usage by folks has past.

But with less light, uptake, demand, we also do not need to add this much either, the point is there is no real risk involved if we do.

Tom Barr